1. Field of the Invention
The present invention relates to a suspension system and oscillating undercarriage for a tracked vehicle.
2. Description of the Related Art
A variety of track systems have been developed for use with heavy duty off road vehicles, such as construction or exploration vehicles. A common track system includes a front idler wheel and a rear drive sprocket over which the continuous track is draped. Another system is known as a triangular track system in which a track frame is pivotally mounted to a pivot shaft on a vehicle. Front and rear idler wheels are mounted at opposing ends of the track frame. The drive sprocket is rotatably mounted on the vehicle above the pivot shaft. A continuous track engages the drive sprocket and the two idler wheels in a triangular configuration. The advantage of the triangular configuration is that the drive sprocket is mounted above the ground surface, thus freeing it from dirt and debris, prolonging its life. Additionally, the drive sprocket construction can be lightened because it is not required to carry a part of the vehicle load.
A distinguishing feature of the triangular track system is that as the track frame rocks about the pivot shaft, the geometry associated with the idler wheels and the drive sprocket changes. For example, as the track frame rocks from the horizontal, the circumference around the idler wheels and drive sprocket is reduced, thus causing slack in the track. Slack in the track is undesirable because it allows the track to become disengaged from either the idler wheels or sprocket or both. In addition, a certain amount of preload tension in the track is desirable to maintain the track, idler wheels and sprocket in engagement. The preload tension should be minimal in value and remain essentially constant to minimize wear on the component parts of the track system. While a spring-loaded idler wheel can take up the slack and maintain the preload tension, such a track system does not provide the fixed axle vehicle with any suspension.
One attempt at providing suspension for a triangular track system is disclosed in U.S. Pat. No. 5,273,126. This system includes a drive sprocket that remains positionally fixed relative to the vehicle body, a rear idler wheel and track-engaging ground rollers that are coupled to, and move with, a swing link that is secured by a spring suspension, and a compensator idler. Accordingly, the suspension is included within the track system itself.
What is needed is a track suspension system that is rugged and durable. What is needed is a suspension system for a tracked vehicle that does not require major redesign of the track assembly. It would be desirable if the vehicle suspension provided a smooth ride, both for operator comfort and for the care of expensive equipment carried by the vehicle. Furthermore, it would be desirable if the vehicle had a track with sufficient surface area to reduce the ground pressure exerted by the vehicle in order to minimize environmental impact.
The present invention provides a track suspension system for a vehicle. The suspension system includes a main axle beam supporting one or more attachment beams extending from the main axle beam toward the front of the vehicle. The attachment beams are connected to the vehicle chassis via a spherical bearing. The main axle beam also contains pivot shafts on both ends, wherein track assemblies are pivotally connected thereto. In addition, the main axle beam is connected through a spherical bearing to a first shock-absorbing member at a first end of the main axle beam and through a spherical bearing to a second shock-absorbing member at a second end of the main axle beam. The other ends of the shock-absorbing members are connected through spherical bearings to the vehicle chassis.
The system further comprises a centralizer that maintains the side-to-side alignment of the main axle beam beneath the vehicle chassis while allowing relative up and down movement. A preferred centralizer is referred to as a side location rod or panhard rod and is coupled to the main axle beam at or near the first end of the main axle beam and to the vehicle chassis adjacent to a second end of the main axle beam. Preferably, spherical bearings are used at the interface between the centralizer and main axle beam and the interface between the centralizer and vehicle chassis. Other suitable centralizers include, without limitation, a watts linkage and a Jacob""s ladder.
The shock absorbing members provide the primary support for the vehicle chassis, and the shock absorbing members may have a variety of configurations, including single or double-sided displacement cylinders or air springs. It is preferable that the shock absorbing members are single or double-sided displacement cylinders, and that they are in fluid communication with an accumulator, wherein the accumulator comprises a gas chamber and a working fluid chamber. The gas chamber and the working fluid chamber are maintained at the same pressure, and typically, the working fluid fills the working fluid chamber and the displacement cylinder. The gas chamber is typically pressurized sufficiently such that the weight of the vehicle is supported at a position approximately halfway through the displacement cylinder range of extension. Alternatively, the system may comprise a hydraulic pressure source in fluid communication with the displacement cylinders for extending and retracting the cylinder.
Each track assembly comprises a track frame that has first and second ends, wherein the track frame is mounted for rocking movement on the pivot shaft at a location between the first and second ends of the track frame. The track assembly further comprises a drive wheel, disposed above and adjacent to the pivot shaft, that engages a track. In addition, an idler wheel link is pivotally mounted to the first end of the track frame and extends upward ending in an upward end. A first idler wheel is rotationally mounted on the idler wheel link, and a second idler wheel is rotationally mounted on the second end of the track frame. In addition, a track extends around the drive wheel, the first idler wheel and the second idler wheel on portions of their respective circumferences. The idler wheel link is further provided with a take up means for moving the first idler wheel away from the pivot shaft to maintain a substantially constant circumference around the idler wheels and drive wheel and a constant tension on the track. The preferred track is a rubber track. The track assembly described above is a preferred example, but other track assemblies may work equally well in association with the present invention and are considered to be within the scope of the invention.